The present invention generally relates to a particular group of monomers and to their use in crack prevention of implanted prostheses. More particularly, the monomers include an active terminal isocyanate group and an active terminal acrylate group, such monomers being reaction products of an aromatic diisocyanate and an acrylate or a methacrylate. These monomers have exceptionally low vapor pressures at room temperature and exhibit a variety of uses including its particular usefulness as a coupling agent or primer coating for applying a crack-preventative composition such as a silicone rubber material to an implantable polymeric surface of a medical prosthesis, the polymeric surface being one that will crack when subjected to implantation for substantial time periods if it is not thus treated.
Reactive monomers or molecules that are easy to handle are generally sought after for a variety of reasons and uses. For example, a reactive monomer that possesses numerous advantageous properties with respect to its reactability is 2-isocyanate ethyl methacrylate, also referred to as isocyanatoethyl methacrylate (IEM), which is available from The Dow Chemical Company as a latent crosslinker for coating and adhesive resins. Such is a difunctional monomer with an aliphatic isocyanate functionality and a vinyl polymerizable double bond. Either end of this molecule can be reacted first, leaving the other functionality for latent reaction, the isocyanate group reacting, for example, with active hydrogen compounds, and the methacrylate functionality, for example, allowing copolymerization with vinyl monomers. Applications for IEM generally fall into three categories: polyisocyanates made by polymerizing the methacrylate group, vinyl functionalized resins made by reacting the isocyanate group with polyfunctional molecules, and polymerizable derivatives made by reacting the isocyanate group with monofunctional reagents. In addition to being useful as a latent crosslinker, IEM is suitable for use as a graft site for making resins suitable for coatings or adhesives.
Although a monomer such as IEM has many outstanding properties and exhibits exceptional versatility and suitability for numerous applications, a monomer such as IEM does have an especially troublesome disadvantage. The 2-isocyanate ethylmethacrylate monomer is extremely difficult to handle due to its high vapor pressure at room temperature, and the monomer is limited to use within fume hoods or glove boxes. Moreover, although such an IEM type of monomer possesses the desired reactive properties referred to hereinabove, the aliphatic nature of the carbon atoms that are alpha to the isocyanate tends to retard the reactivity of the isocyanate, thereby typically requiring a catalyst in order to react the isocyanate. Catalysts that are needed in this regard often poison other catalysts such as platinum that might be required for a particular reaction sequence. Also, the catalysts needed for IEM often preclude co-reactions of free radical polymerized polymers such as silicone rubbers.
Accordingly, there is a need for a monomer or molecule that possesses many of the properties of a molecule such as IEM, but which does not bring with it the extremely difficult handling problems that are associated with a high vapor pressure monomer such as IEM. Furthermore, additional advantageous attributes could be realized if such a monomer exhibited an isocyanate reactivity that is greater than that of a monomer such as IEM and that does not require a catalyst in order to react the isocyanate. Additionally, a monomer such as IEM can be expensive and difficult to synthesize because an isocyanate group has to be formed at its terminal location without disturbing other reactive groups on the reactant molecule.
By the present invention, a monomer is provided which has reactivity properties along the lines of those of a monomer such as IEM, but it has an extremely low vapor pressure, which permits its use in ambient air environments. The monomer includes a terminal isocyanate site and a terminal acrylate or methacrylate site, and it is a reaction product of an aromatic diisocyanate and an acrylate or methacrylate having a reactive hydroxyl group, amide group or the like that reacts with one of the isocyanate groups of the aromatic diisocyanate in order to form the monomer according to this invention. The reaction proceeds readily and inexpensively on a generally equimolar basis. Included in the useful applications of the monomer is its use as a coupling agent or primer, particularly its advantageous properties that enable it to enhance the application of a crack preventative component to a prosthesis having a biocompatible polymeric surface in order to thereby substantially prevent surface fissuring, cracking or crazing which would otherwise be exhibited by the biocompatible polymer under in vivo conditions.
It is accordingly a general object of the present invention to provide an improved monomer having a reactive vinyl moiety and an extremely reactive isocyanate moiety.
Another object of this invention is to provide an improved monomer that is suitable for use as a coupling agent and that exhibits an extremely low vapor pressure at room temperature so that it may used in ambient air environments.
Another object of this invention is to provide an improved method for treating a polymeric material to substantially prevent surface fissuring, cracking or crazing of the polymer under in vivo conditions, which treatment method includes the use of a coupling agent.
Another object of the present invention is to provide an improved method for forming an implantable device which utilizes an advantageous coupling agent having a low vapor pressure.
Another object of the present invention is to provide an improved implantable device that incorporates a coupling agent having a low vapor pressure to pretreat the device for applying a crack preventative component thereto.
These and other objects, features and advantages of this invention will be clearly understood through a consideration of the following detailed description.